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| United States Patent |
5,500,315
|
|
Calvert
, et al.
|
March 19, 1996
|
Processes and compositions for electroless metallization
Abstract
Methods and compositions for electroless metallization. In one aspect, the
invention is characterized by the use of chemical groups capable of
ligating with an electroless metallization catalyst, including use of
ligating groups that are chemically bound to the substrate. In a preferred
aspect, the invention provides a means for selective metallization without
the use of a conventional photoresist patterning sequence, enabling
fabrication of high resolution metal patterns in a direct and convenient
manner.
| Inventors:
|
Calvert; Jeffrey M. (Burke, VA);
Dressick; Walter J. (Fort Washington, MD);
Calabrese; Gary S. (North Andover, MA);
Gulla; Michael (Millis, MA)
|
| Assignee:
|
Rohm & Haas Company (Philadelphia, PA)
|
| Appl. No.:
|
317347 |
| Filed:
|
October 4, 1994 |
| Current U.S. Class: |
430/16; 257/E21.174; 257/E21.175; 427/98.5; 427/99.1; 427/301; 427/304; 427/306; 428/209; 428/420; 430/17; 430/315; 430/324 |
| Intern'l Class: |
G03C 005/58; G03F 007/038 |
| Field of Search: |
430/311,16,17,231,315,324
428/420,209
427/98,304,301,306
|
References Cited
U.S. Patent Documents
| 3671250 | Jun., 1972 | Andrews et al. | 96/88.
|
| 3853589 | Dec., 1974 | Andrews et al. | 117/47.
|
| 4426247 | Jan., 1984 | Tamamura et al. | 156/643.
|
| 4604699 | Aug., 1986 | DeLuca et al. | 427/98.
|
| 4661384 | Apr., 1987 | Sirinyan et al. | 427/304.
|
| 4666735 | May., 1987 | Hoover et al. | 427/43.
|
| 4738869 | Apr., 1988 | Baumgartner | 427/54.
|
| 4746536 | May., 1988 | Ichikawa et al. | 427/54.
|
| 4976990 | Dec., 1990 | Bach et al. | 427/98.
|
| 4981715 | Jan., 1991 | Hirsch et al. | 427/53.
|
| 4996075 | Feb., 1991 | Ogawa et al. | 427/12.
|
| 5045436 | Sep., 1991 | Tieke et al. | 430/315.
|
| 5077085 | Dec., 1991 | Schnur et al. | 427/98.
|
| 5079600 | Jan., 1992 | Schnur et al. | 427/98.
|
| Foreign Patent Documents |
| 1463803 | Feb., 1977 | GB.
| |
Primary Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Goldberg; Robert L.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This is a continuation of application(s) Ser. No. 08/062,706 filed on May
17, 1993 now U.S. Pat. No. 5,389,496, which is a continuation-in-part of
prior applications Ser. No. 07/691,565, filed Apr. 25, 191, now abandoned,
which is a continuation-in-part of Ser. No. 07/022,439, filed Mar. 6, 1987
now U.S. Pat. No. 5,077,085 and Ser. No. 07/182,123, filed Apr. 14, 1988
now U.S. Pat. No. 5,079,600.
Claims
We claim:
1. An article of manufacture comprising an electroless metal deposit in an
image pattern on a substrate, said substrate, at least where coated with
said metal deposit, having bonded to its surface one or more multidentate
chemical groups ligated by coordination bonding other than by
electrostatic interaction with a substantially tin-free, electroless
metallization catalyst.
2. The article of claim 1 where the multidentate chemical groups comprise
one or more moieties selected from the group consisting of aromatic
heterocycle, amino, phosphino, carboxylate and nitrile.
3. The article of claim 1 where the substrate chemical groups comprise one
or more moieties selected from the group of pyridyl and ethylene diamine.
4. The article of claim 1 where the electroless metallization catalyst is a
palladium catalyst.
5. The article of claim 4 where the catalyst is selected from the group
consisting of bis(benzonitrile) palladium dichloride, palladium dichloride
and salts of PdCl.sub.4.sup.2-.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to processes and compositions for electroless
metallization and related articles of manufacture and, more particularly,
the invention relates to the use of substrate chemical groups capable of
ligating with a variety of electroless metallization catalysts, including
tin-free catalysts, and selective electroless plating through the use of
such ligating groups.
2. Background Art
Electroless metallization procedures typically require multiple and complex
processing steps. See, for example, reviews of electroless plating in C.
R. Shipley, Jr., Plating and Surface Finishing, vol. 71, pp. 92-99 (1984);
and Metal Finishing Guidebook and Directory, vol. 86, published by Metals
and Plastics Publications, Inc. (1988), both incorporated herein by
reference. One typical procedure for metallization of polymeric substrates
employs a colloidal palladium-tin catalyst in the following sequence: (1)
pre-cleaning the substrate surface; (2) microetching, for example with a
chromic-based solution; (3) conditioning the etched substrate surface; (4)
adsorption of the palladium-tin catalyst onto the conditioned surface; (5)
treatment with an accelerator to modify and activate the absorbed
catalyst; and (6) treatment with an electroless plating solution. See, for
example, U.S. Pat. Nos. 4,061,588 and 3,011,920. A number of fundamental
studies have been performed on this and related electroless procedures.
See, for example, J. Horkans, J. Electrochem. Soc., 130, 311 (1983); T.
Osaka, et al., J. Electrochem. Soc., 127, 1021 (1980); R. Cohen, et al.,
J. Electrochem. Soc., 120, 502 (1973); and N. Feldstein, et al., J.
Electrochem. Soc., 119, 668 and 1486 (1972).
While the exact composition and structure of such a Pd/Sn catalyst have not
been confirmed, and the detailed mechanism by which a Pd/Sn colloid
adheres to a substrate is not fully understood, the following is known
and/or currently postulated. A palladium-tin electroless catalyst
typically is generated by mixing multi-molar stannous chloride and a
palladium chloride in an acidic aqueous solution containing excess
chloride ion. Sn(II) reduces the Pd(II) species, likely via an
inner-sphere redox reaction in a Pd/Sn complex, resulting in a colloidal
suspension with a dense metallic core within a less dense tin polymer
layer. The central portion of the colloid is composed of an intermetallic
compound of stoichiometry reported to be Pd.sub.3 Sn. This inner core is
believed to be a cluster containing up to 20 atoms with palladium
principally in the zero and +1 oxidation states. This inner core is the
actual catalyst in the initial metal reduction that leads to electroless
metal deposition.
Surrounding this core is a layer of hydrolyzed stannous and stannic species
that forms an outer shell of oxy- and/or hydroxy-bridged oligomers and
polymers together with associated chloride ions. This layer is known as
beta-stannic acid. The composition of the colloidal suspension contains a
high concentration (multi-molar excess) of stannous ions relative to Pd
which continue to hydrolyze and form higher oligomers on the outer surface
of the initially formed colloidal particles. Consequently the thickness
and degree of polymerization of the outer tin shell changes over time. The
resultant colloidal particle has a net negative charge.
Adhesive properties of the outerpolymeric outer shell attach the catalyst
to the substrate to be plated, known in the art as the activation process.
The negative charge of the outer tin shell prevents aggregation of the
colloids permitting individual attachment to the substrate. The reducing
power of the Sn(II) acts as an anti-oxidant and protective layer that
maintains the catalytic core in the low valent Pd state necessary to
initiate plating. Activation is followed by an acceleration step whereby
the catalyst core is exposed. Acceleration can be achieved by a variety of
means, for instance by "subtractive" type means of dissolving the stannous
protective layer at high chloride ion concentrations to form soluble
SnCl.sub.4.sup.2-, or by oxidizing the shell to the more soluble Sn(IV) by
exposure to oxygen from the ambient. "Additive" type acceleration
sequences are also known. For example, European Patent Application
90105228.2 discloses the application of an acidic solution of PdCl.sub.2
to the intact adsorbed colloid. The stannous polymer layer of the particle
reduces the palladium ion in situ to form a metallic Pd deposit on which
plating can occur. After activation, the substrate is immersed in an
electroless plating solution. A typical electroless metal plating solution
comprises a soluble ion of the metal to be deposited, a reducing agent and
such other ligands, salts and additives that are required to obtain a
stable bath having the desired plating rate, deposit morphology and other
characteristics. Common reductants include hypophosphite ion (H.sub.2
PO.sub.2.sup.-), formaldehyde, hydrazine or dimethylamine-borane. The
reductant reacts irreversibly at the catalyst core to produce an active
hydrogen species, presumably a palladium hydride. The surface hydrogen is
also a potent reductant which transfers electrons to the soluble metal
complex in the bath and produces a metal deposit on top of the catalyst,
which eventually covers the core sufficiently to block access to the
external solution. For certain deposits, such as copper, nickel and
cobalt, the nascent layer can itself become "charged" with hydrogen and
continue to reduce metal ion to metal, leading to "autocatalytic" build-up
of an electroless deposit onto the activated surface. In a competitive
reaction, surface hydrogen atoms combine to evolve H.sub.2 gas. This
latter reaction has never been completely suppressed. Therefore, not all
available reducing equivalents in the electroless bath can be used for
metal deposition. For a properly catalyzed surface, the choice of
electroless metal plating solution is determined by the desired properties
of the deposit, such as conductivity, magnetic properties, ductility,
grain size and structure, and corrosion resistance.
Such a palladium-tin catalyst system presents a number of limitations. At a
minimum three steps are required--activation, acceleration and plating.
Often substrate pre-treatment and other additional steps are necessary to
provide uniform plating. The colloidal catalyst also is readily oxidized
and stannous ions must be replenished by regular addition of Sn(II) salts.
Further, the colloid size may fix packing density thereby making difficult
uniform plating of ultra-small objects, e.g. objects less than about 1,000
angstroms in size. Subtractive-type acceleration requires a precise and
often difficult balance of exposing the palladium core without dissolving
the portion of the stannous shell that provides adherence to the substrate
surface. Further, substrate adhesion of a Pd/Sn catalyst has been found to
be a relatively non-specific phenomenon. For example, the catalyst will
only weakly adhere to a smooth photoresist coating, requiring a pre-etch
step to provide a more textured surface and thereby increasing processing
time and costs. For many situations, such as high resolution lithography,
such pre-etching is not feasible. Further, a number of materials are
"colloidophobic", i.e. materials to which a Pd/Sn catalyst does not
adsorb. These materials include silica, certain metals and some plastics.
Recently, several electroless plating procedures have been reported, the
procedures generally employing a palladium catalyst and a polyacrylic acid
or polyacrylamide substrate coating. See, U.S. Pat. Nos. 4,981,715 and
4,701,351; and Jackson, J. Electrochem. Soc., 135, 3172-3173 (1988), all
incorporated herein by reference.
A common method for producing a patterned metallized image includes use of
a photoresist coating. In an additive metallization approach, photoresist
is applied to a substrate surface; the resist is exposed to provide
selectively soluble portions of the photoresist coating; a developer is
applied to bare selected portions of the substrate surface; those selected
portions are metallized; and the remaining resist stripped from the
substrate surface. See, generally, Coombs, Printed Circuits Handbook, ch.
11 (McGraw Hill 1988), incorporated herein by reference. A print and etch
procedure is a subtractive approach where in the case of circuit line
fabrication, a copper layer is selectively chemically etched through use
of a photoresist to define the circuit traces. For higher performance
applications, it is crucial that circuit sidewalls be uniform and
essentially vertical. Resolution limits exist with a print and etch
sequence, however, which are inherent in the subtractive nature of this
approach.
SUMMARY OF THE INVENTION
The present invention comprises an electroless metal plating-catalyst
system that overcomes many of the limitations of prior systems. In one
aspect of the invention, a process is provided comprising steps of
providing a substrate comprising one or more chemical groups capable of
ligating to an electroless plating catalyst, at least a portion of the
chemical groups being chemically bonded to the substrate; contacting the
substrate with the electroless metal plating catalyst; and contacting the
substrate with an electroless metal plating solution to form a metal
deposit on the substrate. The chemical groups can be, for example,
covalently bonded to the substrate.
In another preferred aspect, the invention provides a process for selective
electroless metallization, comprising steps of selectively modifying the
reactivity of a substrate to an electroless metallization catalyst;
contacting the substrate with the electroless metallization catalyst; and
contacting the substrate with an electroless metallization solution to
form a selective electroless deposit on the substrate. The substrate
reactivity can be modified by selective treatment of catalyst ligating
groups or precursors thereof on the substrate, for example by
isomerization, photocleavage or other transformation of the ligating or
precursor groups. Such-direct modification enables selective plating in a
much more direct and convenient manner than prior selective plating
techniques. Specifically, the present invention provides selective
electroless plating without the use of a photoresist or an adsorption type
tin-containing plating catalyst.
The one or more chemical groups capable of binding to the electroless
catalyst may be provided by a variety of means. The material of
construction of the substrate may comprise the catalyst ligating groups,
for example a polyvinylpyridine substrate or an alumina substrate.
Substrates that do not inherently comprise such ligating groups may be
treated to provide the groups. For example, a source of the ligating
groups may be formulated as a material of construction of the substrate.
Alternatively, a substrate may comprise suitable precursor groups which
upon appropriate treatment provide the necessary catalyst ligating groups.
Such treatment will vary with the particular ligating group and includes,
for example, thermolysis, treatment with chemical reagents, photochemical
modification such as isomerization or photocleavage of a precursor group,
and plasma etching. Further, such treatment methods can provide precursor
groups, such as hydroxyl, carboxyl, amino and others to which a ligating
group can be bonded. Still further, the ligating chemical groups or
precursors thereof may be provided by contacting at least portions of the
substrate surface with a compound or composition comprising the ligating
groups, the ligating groups preferably adhering well to the substrate
surface, for instance by chemical and/or physical interaction. If chemical
bond formation is employed as the substrate adherence means, substrate
adhesion and catalyst ligation functions may be performed by application
of a single molecule or, alternatively, by application of multiple
molecules with subsequent linkage therebetween.
A variety of metallization catalysts may be employed, including tin-free
catalysts, with palladium (II) compounds and compositions preferred for
the generally superior catalytic activity those catalysts provide. A
substrate is preferably treated with a solution of the metallization
catalyst, for example an aqueous solution or a solution of an organic
solvent. The catalyst solution preferably comprises other materials such
as ancillary ligands, salts and buffers to enhance the stability of the
catalyst solution and thereby to provide suitable catalyst activity as
well as convenient use and storage of the solution.
The substrate to be electrolessly plated according to the present invention
may be a variety of materials such as a conductive material, a
semiconductor material, an electrically nonconductive material, and more
specifically, electronic packaging substrates such as a printed circuit
board or a precursor thereof. In a preferred aspect, the invention is
employed to metallize lipid tubule microstructures. It is believed that a
wide variety of metals may be electrolessly plated in accordance with the
present invention, for example cobalt, nickel, copper, gold, palladium and
various alloys.
As is apparent to those skilled in the art, notable advantages of the
invention include an electroless catalyst system that requires fewer and
simpler processing steps in comparison to current Pd/Sn colloid catalyst
adsorption based systems; use of more stable and convenient catalysts,
including tin-free catalysts; and improved catalyst adhesion to a
substrate allowing plating of more dense initiation and of greater
uniformity and selectivity. The invention also provides selective
patterning of substrate ligating groups, thereby enabling a selective
metal deposit without the use of a conventional photoresist patterning
sequence.
The terms-"ligate" or "ligating" or "ligation", as used herein in reference
to the interaction between an electroless metallization catalyst and the
substrate chemical groups of the invention, refers to any attraction,
binding, complexing, chelating or sequestering, whatever the nature or
extent of such attraction, binding, complexing, chelating or sequestering,
between the catalyst and the substrate chemical group.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Many substrates or substrate surfaces capable of being plated according to
the present invention intrinsically contain chemical groups, or
appropriate precursors of chemical groups, that are able to ligate an
electroless plating catalyst. For example, a polyvinylpyridine film
intrinsically contains such chemical groups with the pendant pyridine
serving as the catalyst ligating group. As discussed herein, the pyridyl
group has been found to be a particularly preferred ligating group for a
palladium catalyst. For a discussion of the pyridyl moiety as a ligating
group, see Calvert, et al., Inorganic Chemistry, 21, 3978 (1982),
incorporated herein by reference. Similarly, a substrate comprising
aluminum oxide will bind a palladium catalyst by the AlO and AlOH groups
of the alumina. Further, the ligating material need not be the sole
component of the substrate. Thus, the ligating material may be physically
blended as one of multiple components comprising the substrate if
sufficient ligating moieties are accessible at the substrate surface to
ligate to the catalyst.
A possible shortcoming of such a blending approach is that incorporation of
large quantities of a second material may impair the film-forming or other
properties of the bulk material. A potential solution to this problem is
to incorporate a surfactant form of the ligating component into the bulk
material by proper choice of the relative solubility/polarity
characteristics of the ligating component and the surfactant. By
incorporating a small percentage of the surfactant into the bulk, a high
surface concentration of the ligating component could be produced. An
analogous approach has been employed in the photoresist arts, where a
small quantity of surfactant is formulated into the resist to enhance film
planarity by reducing the surface tension through a high surface
concentration of surfactant.
Many substrates that do not inherently comprise suitable ligating groups
may be readily modified to possess the necessary ligating groups.
Substrate modification methods include, but are not limited to,
thermolysis, reaction of the surface with one or more chemical reagents,
irradiation with photons or ions, vapor phase modification, graft
polymerization, x-ray and nuclear radiation treatment or, more generally,
any treatment that effects the desired conversion of the substrate. One
potential modification sequence provides hydrolysis of a polyimide surface
and reacting the hydrolyzed surface with a silane reagent possessing a
suitable ligating group, such as .beta.-trimethoxysilylethyl-2-pyridine.
Another method provides chemically etching a polyethylene surface with a
Cr.sub.2 O.sub.7.sup.2- solution to provide hydroxyl groups on the
substrate surface. The hydroxyl groups should then condense with a
suitable compound containing a ligating group, for example nicotinoyl
chloride with its pyridyl ligating group. Some of the surface substrate
modification methods permit convenient selective treatment of a substrate
surface. For example, if a surface can undergo a photochemical conversion
to reveal a ligating group, that surface can be exposed to masked
radiation and directly produce a pattern of catalyst binding sites. After
treatment with a suitable catalyst, the patterned catalyst surface can
then be electrolessly metallized to produce a negative tone image of the
mask employed.
Rather than directly modifying the substrate, the substrate may be imparted
with suitable ligating groups by indirect modification of the surface. For
example, a substrate may be coated with one or more film layers, each
layer comprising one or more suitable ligating agents. The film layer
preferably adheres well to the substrate, for example by containing a
functional group that will chemically and/or physically adhere to the
substrate.
The adhesive and ligation functions of such a film may be performed by
application of a single molecule or, alternatively, by application of
multiple molecules with subsequent linkage between each of the molecules.
For example, .beta.-trimethoxysilylethyl-2-pyridine provides both ligating
and substrate-adherent functionalities. The alkoxysilane group can
chemically bind the compound to a substrate. For instance, the
trimethoxysilyl group reacts with surface hydroxyl (silanol) functions of
a quartz substrate, displacing methanol to directly bond to the substrate.
The thus bound pyridyl moiety of the silylpyridyl molecule serves as a
ligand for chelating with the plating catalyst.
As noted, the adhesive and ligating functions may be performed by multiple
chemical groups with bond formation or other linkage between each of the
groups. The linkage connecting the multiple functional groups may be of
variable length and chemical composition. Examples include
3-(trimethoxysilyl) propylamine and a quinoline-8-sulfonic acid chloride.
The aminosilane is applied as the substrate adsorbent. The coated surface
is then reacted with a quinoline-8-sulfonic acid chloride, the SO.sub.2 Cl
group coupling to the amine group of the coated surface to form a
sulfonamide linkage, and the quinolinic group serving as a catalyst
ligation moiety. Similarly, 3-(trimethoxysilyl) propylamine can be applied
to a substrate and then reacted with the acid chloride group of
4,4'-dicarbonyl chloride-2,2'-bipyridine to form an amide linkage. The
pyridyl moieties of this complex serve as catalyst ligating groups. Other
silyl amines can be condensed in a similar manner, for example
3-(triethoxysilyl) propylamine. Another sequence provides condensing the
hydroxyl groups of a chemically etched polyethylene substrate with a
suitable ligating precursor, for example, 3-(trimethoxysilyl)propylamine,
which after formation of the oxygen-silyl bond by methanol displacement,
the amino group can condense with a suitable ligating compound such as
nicotinoyl chloride.
A ligating chemical group comprising a radiation sensitive chromophore can
provide selective photochemical patterning and metallization where
selective photolysis or radiation ablation modifies the chemical groups on
the substrate surface to substantially reduce or eliminate ligating
ability in the selected film surface areas. Subsequent exposure to the
plating catalyst and metallization solutions provides a positive tone
image of the photomask employed. For example, the pyridyl group of
.beta.-trimethoxysilylethyl-2-pyridine serves as a chromophore for
convenient patterning and subsequent selective metallization of the
substrate surface through microlithographic techniques.
Analogously, a ligating film can be employed where selective photolysis
transforms a non-ligating group within the film into a ligating group. For
example, azoxybenzene derivatives photoisomerize from a weakly or
non-ligating azoxybenzene group to the ligating 2-hydroxyazobenzene group.
The chelating ability of 2-hydroxyazobenzene and
2-(2-pyridylazo)-1-naphthol has been described in Calabrese, et al.,
Inorq. Chem., 22, 3076 (1983), incorporated herein by reference. The
Photo-Fries reaction is another potential means to provide suitable
ligating groups. By this reaction, for example, polyacetoxystyrene can be
irradiated with ultraviolet radiation to provide the ligating
2-hydroxyacetophenone moiety.
Depending on the nature of the radiation-sensitive materials employed, such
transformations may be accomplished with a variety of exposure sources and
imaging tools. For example, ultraviolet or visible light will be suitable
for certain transformations, while other transformation may require
exposure sources such as electron beam or x-ray treatment. Such energy
sources can be provided by image tools known to those in the art, for
example ultraviolet contact printers and projection steppers, electron
beam writers and x-ray proximity printers.
For such patterning of a ligating film, the film preferably is an ultrathin
film, which is a film defined herein to mean a film of a composite
thickness of between about ten molecular layers and a single molecular
(monomolecular) layer. Such a film can be formed through dip coating or
vapor phase deposition procedures as are known in the art. A ligating film
composed of multiple layers of ligating groups may not provide highly
selective plating. Radiation exposure may fail to penetrate sufficiently
the entire thickness of a multiple layer film leaving intact ligating
groups in undesired substrate surface areas, thereby resulting in
non-selective plating. As irradiation can readily penetrate through the
thickness of an ultrathin film, such a film can be patterned with greater
precision resulting in greater image resolution.
As described above, the invention provides a substrate surface containing a
chemical functional group capable of binding metallization catalysts from
solution. One way of binding a catalyst to a surface is by a metal-ligand
complexation, or ligation reaction. Though not wishing to be bound by
theory, the ability of a substrate ligand L to bind an electroless
catalyst, for example a palladium (II) catalyst, should be readily
determined by examining the formation equilibrium constant K.sub.f for the
generalized complexation reaction (I):
Pd.sup.2+ +L<-->PdL.sup.2+ (I)
wherein, K.sub.f is equal to the ratio of concentration of products to
reactants in reaction (I), i.e.,
##EQU1##
Large values of K.sub.f would indicate strong, or essentially
irreversible, binding of the catalyst to the ligand. See, generally, A.
Martell, et al., "Critical Stability Constants", Plenum Press, New York
(1975), where examples of complexation reactions have been tabulated.
While little data has been reported for palladium (II) ligation reactions,
the general trends for complexation reactions can be obtained by examining
the formation constant values for Ni(II). Palladium is directly below
nickel in the periodic table and has similar coordination properties. The
results with nickel ion shows that through a chelate effect a multidentate
ligand (chelate) provides a greater K.sub.f than a corresponding
monodentate group, where the term monodentate group refers to a chemical
group that can provide only one ligand binding site, and the term
multidentate group refers to chemical group or groups that can provide
greater than one ligand binding site. For example, chelation of Ni(II) by
2,2'-bipyridine results in a complex that is 10,000 times more stable than
a pyridine complex, and 30 times more stable than a bis-pyridine complex.
Further, it is believed that a higher K.sub.f provides a metal
deposit-with relatively greater adhesion to a substrate upon subsequent
metallization.
Thus, a bipyridyl is preferred over a monopyridyl for the relatively
stronger bond the bipyridyl forms with an electroless metallization
catalyst and the higher quality metal deposit thereby provided. Use of
suitable multidentate ligating groups has enabled deposition of thick
adherent metal plates, including metal plates of thickness equal to and
greater than about 2500 angstroms on smooth, unetched surfaces. In
addition to bipyridyl, numerous other multidentate groups should also
serve as suitable ligating groups, for example 2,2':6,2''-terpyridine,
oxalate, ethylene diamine, 8-hydroxyquinoline and 1,10-phenanthroline.
Organophosphines, nitriles, carboxylates and thiols should also ligate
well, i.e. exhibit a significant K.sub.f, with a palladium electroless
metallization catalyst. For example, 3-mercaptopropyltriethoxysilane,
2-(diphenylphosphino)ethyltriethoxysilane, and cyanomethylphenyl
trimethoxysilane should serve as suitable catalyst ligating groups in
accordance with the invention. Also preferred are ligating groups with
antibonding (pi*) orbitals in the ligand, for example aromatic
heterocycles such as pyridine and other nitrogen containing aromatics.
Such groups give rise to dpi.fwdarw.pi* backbonding interactions that
favor complex formation. It has thus been found that a benzyl chloride
group provides poor ligating ability whereas an alkylpyridyl provides good
ligation to an electroless catalyst.
A variety of compounds may be employed as the electroless catalyst in
accordance with the invention, such as palladium, platinum, rhodium,
iridium, nickel, copper, silver and gold. Palladium or
palladium-containing compounds and compositions generally provide superior
catalytic activity and therefore are preferred. Particularly preferred
palladium species include bis-(benzonitrile)palladium dichloride,
palladium dichloride and Na.sub.2 PdCl.sub.4. Other salts of
PdCl.sub.4.sup.2- should also be suitable, such as potassium and
tetraethylammonium salts.
The electroless metallization catalysts useful in the processes of the
invention are preferably applied to the substrate as a solution, for
example as an aqueous solution or a solution of an organic solvent.
Suitable organics include dimethylformamide, toluene, tetrahydrofuran, and
other solvents in which the metallization catalyst is soluble at effective
concentrations.
Means for contacting a substrate with a catalyst solution may vary widely
and include immersion of the substrate in a solution as well as a spray
application. The catalyst solution contact time required to provide
complete metallization of the contact area can vary with catalyst solution
composition and age.
A variety of catalyst solutions have been successfully employed, with
solutions stabilized against decomposition preferred. Thus, the catalyst
solution may comprise ancillary ligands, salts, buffers and other
materials to enhance catalyst stability. Though again not wishing to be
bound by theory, it is believed many of the catalyst solutions useful in
the present invention decompose over time by oligomerization and formation
of insoluble oxo-compounds, for example as reported by L. Rasmussen and C.
Jorgenson, Acta. Chem. Scand., 22, 2313 (1986). It is believed the
presence of catalyst oligomers in the catalyst solution can affect the
ability of the catalyst to induce metallization and/or inhibit selectivity
of metallization of a patterned substrate. For example, as such catalyst
oligomers increase in molecular weight, their solubilities decrease and
precipitation of the catalyst can occur.
Suitable agents for stabilizing a catalyst solution can vary with the
particular catalyst employed, as is apparent to those skilled in the art.
For instance, a metallization catalyst of PdCl.sub.4.sup.2- can be
stabilized in aqueous solution by addition of excess chloride ion and
decreasing pH to inhibit formation of oxo-bridged oligomers of the
catalyst, of proposed structures such as Cl.sub.3 PdOPdCl.sub.2 (H.sub.2
O).sup.3-, and Cl.sub.3 PdOPdCl.sub.3.sup.4-. This is supported by the
greater stability of catalyst solutions comprising sufficient
concentrations of sodium chloride or tetraethylammonium chloride (TEACl)
relative to the stability of PdCl.sub.4.sup.2- solutions not containing
such agents. Such catalyst stabilization can be accomplished by adjustment
of chloride ion concentration during preparation of the catalyst solution,
or by adjustment of chloride ion concentration after the catalyst solution
has attained full catalytic activity. In addition to chloride, other
anions that prevent the formation of catalyst oligomers should also be
suitable agents for stabilizing a catalyst solution, for example bromide
and iodide ions.
Cation effects have also been observed. For example, suitable use of sodium
chloride with Na.sub.2 PdCl.sub.4 provides an active and stablilized
catalyst solution. Replacing sodium chloride with ammonium chloride in
such a solution, however, results in a solution with little or no activity
as a metallization catalyst. In this case, it is believed that the lack of
catalytic activity may be the result of the formation of stable cis- or
trans-(NH.sub.3).sub.2 PdCl.sub.2 species in solution. Replacing sodium
chloride with TEACl provides a solution that requires a shorter induction
period to reach full activity, and once active remains selective and
stable only for a few days. It is further noted that while a number of
cations may be suitable, cation selection may be dictated by the specific
metallization process. For example, for advanced microelectronic
applications, use of sodium ions generally is avoided if possible and,
therefore, use of TEACl as a catalyst solution stabilizer may be
preferred.
It also has been found that catalyst solutions of higher (less acidic) pH,
e.g. pH of greater than 4, can be stabilized with a suitable buffer
solution. Preferably, pH of a catalyst solution is controlled by a buffer
component which does not appreciably coordinate with the metallization
catalyst. For a Pd(II) metallization catalyst, a preferred buffering agent
is 2-(N-morpholino)ethane sulfonic acid, referred to herein as MES,
available from the Aldrich Chemical Company. This buffer has a pK.sub.a of
6.15 and has been described in Good, et al., Biochemistry, 5(2), pp.
467-477 (1966).
Additionally, it has been found that solution preparation methods can
affect the stability and metallization activity of a catalyst solution
useful in the invention. For example, the catalyst solutions disclosed in
Examples 16 and 17 herein are prepared using approximately equivalent
initial quantities of acetate buffer, sodium chloride and Na.sub.2
PdCl.sub.4 .times.3H.sub.2 O. In Example 16 herein, an aqueous catalyst
solution comprising NaCl and Na.sub.2 PdCl.sub.4 .times.3H.sub.2 O reaches
full activity as a metallization catalyst about 24 hours after preparation
at room temperature. Addition of a prescribed amount of acetate buffer to
this active solution maintains its catalytic activity. In contrast,
preparation of a catalyst solution as described in Example 17 herein by
simultaneous mixing of acetate buffer, NaCl and Na.sub.2 PdCl.sub.4
.times.3H.sub.2 O in aqueous solution yields a catalyst solution which
requires about 11 days to reach full activity as a metallization catalyst.
It also has been found that components of a catalyst solution can compete
with the catalyst for binding with substrate ligating sites. For example,
for 4,4'-(di(carboxylic
acid-(N-3-(trimethoxysilyl)propyl)amide))-2,2'bipyridine, the pK.sub.a
values of the pyridyl groups are about 4.44 and 2.6, for mono- and
di-protonation respectively. See, K. Nakamoto, J. Phys. Chem., 64, 1420
(1960). Thus, in the case of a PdCl.sub.2 /HCl (aq) catalyst solution, HCl
may protonate the pyridyl groups and effectively compete for these sites
with the palladium catalyst. While electrostatic interactions may still
occur between the metallization catalyst and such a protonated ligating
group, coordination type binding will be substantially reduced. It has
thus been found that elimination of such ligation competitors from a
catalyst solution increases coordination type binding of the catalyst to
the substrate ligation functionality.
A wide variety of substrates may be used in accordance with the invention.
For example, the substrate may comprise a conductive material such as
tungsten or copper, e.g. a copper clad printed circuit board; a
semiconductor material such as doped silicon; a dielectric material such
as polymeric substrates or ceramic substrates used in electronics
applications, and others such as a photoresist coating and glass and
quartz substrates. Similarly, a variety of metals may be plated according
to the invention including cobalt, nickel, copper, gold, palladium and
alloys thereof, and other alloys such as the nickel-iron-boron alloy
identified as permalloy. Suitable commercial electroless metallization
baths include the nickel electroless plating solution identified as
Niposit 468 and sold by the Shipley Company of Newton, Mass.
The processes of the invention are useful for virtually any electroless
metallization process, such as electroless plating in printed circuit and
printed circuit board manufacture, including metallization of through
holes surfaces in double-sided or multilayer printed circuit boards;
plating on ceramic materials such as ceramic resistors and ceramic circuit
boards; and plating of integrated circuits. More specifically with respect
to the metallization of printed circuit board through-holes, the present
invention provides in general contacting the nonconductive through-hole
walls with a compound or composition comprising electroless catalyst
ligating groups. The ligating compound or composition can be admixed with
a liquid carrier, and the through-holes surfaces treated with such
admixture. After such conditioning, the treated through-holes surfaces are
contacted with a suitable electroless catalyst (e.g., the catalyst
solution described in Example 12 herein) and then the hole walls
metallized according to standard procedures. Electroless nickel or copper
plating of through hole walls is common.
The present invention is particularly useful for fabricating circuit lines
in electronic printed boards. Electroless plating is an additive process
enabling fabrication of high resolution circuit traces with nearly
vertical sidewalls. The present invention permits fabrication of high
resolution circuit lines without the use of a photoresist patterning
sequence. For example, as discussed above, suitable ligating groups or
precursors thereof can be selectively modified to provide ligating groups
in a selective pattern on a substrate surface. Upon subsequent
metallization, a metallized patterned image is provided.
The processes of the invention are also useful to metallize lipid tubule
microstructures, which are hollow cylindrical structures composed of up to
approximately ten bilayers. Characteristic diameters are between about 0.2
to 0.3 microns and wall thicknesses are between about 5 to 50 nanometers.
It is believed the exposed phosphocholine head groups or phosphate groups
of the lipid can serve as catalyst ligating groups.
As described in U.S. Pat. No. 4,911,981, incorporated herein by reference,
numerous applications for metallized tubules and metallized tubule
composite materials are known, including absorbers of electromagnetic
radiation, electron emissive surfaces and controlled release reagents.
Prior lipid metallization procedures generally require numerous processing
steps, resulting in breakage and considerable reduction in aspect ratios
from the as-formed tubules to the metal-coated product. Preservation of
the tubules aspect ratio during the metallization process is highly
desired for many applications of the microstructures. Metallization in
accordance with the present invention saves processing time and steps
relative to prior systems, and thus can lead to preservation of the aspect
ratios of the tubules.
The invention will be better understood by reference to the following
examples.
GENERAL COMMENTS
In the following Examples, all contact angle measurements were made with
water by the sessile drop method with a water drop and an NRL Zisman-type
contact angle goniometer. Ultraviolet absorption data was recorded on a
Cary 2400 Spectrophotometer. For measurements of a film on a silica slide,
molar absorption coefficients (.epsilon.) were calculated from measured
absorbance values based on a surface concentration of 10M and a film
pathlength of 2.times. 10.sup.-7 cm. Nitrogen gas used for drying was
filtered prior to use by passing through a 0.22 .mu.m filter. All water
was deionized.
The following terms when capitalized in the Examples have the following
meanings.
"Standard Cleaning Method" means immersing the substrate in a solution of
1:1 v/v concentrated HCl:methanol for 30 minutes. The substrate is water
rinsed and immersed in concentrated sulfuric acid for 30 minutes, and then
transferred to a container of boiling water and stored therein until use.
Immediately prior to use, the clean substrate is removed from the boiling
water bath and dried with nitrogen or, alternatively dipped in acetone.
"100% Co Metallization Bath" means a bath prepared as follows. 6.0 g of
COCl.sub.2 6H.sub.2 O, 10.0 g NH.sub.4 Cl and 9.8 g
ethylenediaminetetraacetic acid disodium salt are dissolved in 150 mL of
deionized water and the pH brought to 8.2 by addition of 1M NaOH (aq)
solution. Added to three volumes of the Co solution is one volume of a
solution consisting of 8.0 g of dimethylamine borane complex in 100 mL of
water. "50% Metallization Bath" means a bath prepared by diluting one
volume of the 100% Metallization Bath with one volume of water. "25%
Metallization Bath" means a bath prepared by diluting one volume of the
100% Metallization Bath with three volumes of water.
"MES Buffer Solution" means a solution prepared as follows. 2.13 g
MES.times.H.sub.2 O solid is added to 50 mL water with stirring until
dissolution. The pH of the solution is adjusted to 4.9 to 5.0 by dropwise
addition of dilute NaOH. The solution is diluted to 100 mL to produce the
final buffer. This solution has a MES concentration of 0.1M and is
referred to herein as MES Buffer Solution A. MES Buffer Solutions B and C
were prepared in a similar manner to MES Buffer Solution A, except that
the pH of these solutions are 5.7 and 6.4, respectively.
EXAMPLE 1
This example illustrates application of a ligating layer on a substrate
surface by dip coating.
A one-inch square fused silica slide (ESCO Products or Dell Optics) was
cleaned by the Standard Cleaning Method. Contact angle of 5.degree. was
obtained indicating a clean hydrophilic substrate surface. The slide was
dried under nitrogen and placed in a glass holder which permitted exposure
of both faces of the slide. The assembly was placed in a beaker containing
250 mL of a toluene solution 1.0 mM in acetic acid and further containing
1% (v/v) .beta.-trimethoxysilylethyl-2-pyridine (available from Huls
America--Petrarch Systems). The solution was heated for about 40 minutes
until reaching temperature of about 65.degree. C. The solution remained
clear and colorless throughout heating. The slide was removed from the
solution and rinsed twice in toluene. The slide was then immediately baked
for 3 minutes at 120.degree. C. on the surface of a hotplate to complete
attachment of the silane compound. After heating, the slide had a contact
angle of 45.degree. indicating binding of the more hydrophobic silane
compound to the hydrophilic quartz surface. Ultraviolet absorption
spectrum of the thus coated slide versus a reference of an uncoated fused
silica slide was taken. Absorption maxima were observed at 200 nm and 260
nm with .epsilon.=4900 M.sup.-1 cm.sup.-1 and 3700M.sup.-1 cm.sup.-1,
respectively. Correspondence between this spectrum and the spectrum of
.beta.-trimethoxysilylethyl-2-pyridine in acetonitrile confirmed the
binding of the silane compound to the fused silica surface. Calculations
based on the relative intensities of the bands of the surface and solution
analogs indicate an average surface coverage of approximately one
molecular layer of the silane compound.
EXAMPLE 2
This example illustrates application of a ligating film on a substrate
surface by spin coating.
A one inch square fused silica slide was cleaned by the Standard Cleaning
Method and dried as in Example 1. The slide was placed on the vacuum chuck
of a Headway Research Standard Model Spincoater. The top surface of the
slide was completely covered with a methanol solution 1.0 mM in acetic
acid and further containing 1% (v/v)
.beta.-trimethoxysilylethyl-2-pyridine. Excess solution was removed by
spinning the slide at 6000 rpm for 30 seconds. The slide was then baked
for 3 minutes at 120.degree. C. on the surface of a hotplate. After
heating, the slide provided a contact angle of 44.degree.. The ultraviolet
absorption spectrum was qualitatively similar to that of the coated slide
prepared in Example 1 although the spectral bands were more intense and
broader than corresponding bands of the Example 1 spectrum, consistent
with bulk film formation in this case.
EXAMPLE 3
This example illustrates stripping of the outer layers of the bulk film to
produce a surface film layer of thickness of between one and several
molecular layers.
The coated silica slide produced in Example 2 was placed in a glass holder
which permitted exposure of both faces of the slide. The assembly was
immersed in tetrahydrofuran, and the solution was brought to a boil over
0.5 hour. The slide was removed from the solution, rinsed with room
temperature tetrahydrofuran and dried under nitrogen. Ultraviolet
absorption spectrum was comparable to the spectrum of the slide prepared
in Example 1, indicating removal of the outer layers of the film to
produce an ultrathin film on the substrate of thickness of one or several
molecules.
EXAMPLE 4
This example illustrates in situ formation of a ligating film precursor
with subsequent attachment of the same to a substrate surface.
The ligating precursor was 4,4'-dicarbonyl chloride-2,2'-bipyridine. This
compound was prepared by oxidation of 4,4'-dimethyl-2,2'-bipyridine
(Aldrich Chemical Co.) with acidic potassium permanganate to
4,4'-dicarboxy-2,2'-bipyridine, as described in A. Sargeson et al., Aust.
J. Chem., 39, 1053 (1986), incorporated herein by reference. A flask was
charged with 3.5 g (1.39 mM) of this dicarboxy compound and 60 mL toluene
(Aldrich Sure Seal), and then 50 mL (68.5 mM) of thionyl chloride (Aldrich
Gold Label) was quickly added. The flask was outfitted with a reflux
condenser with a CaSO.sub.4 drying tube and the mixture refluxed for 6
hours. Virtually all of the initially insoluble material dissolved during
reflux to provide a slightly cloudy yellow solution. The solution was
cooled to room temperature and filtered through a fritted glass funnel.
The filtrate was concentrated under reduced pressure, and the resulting
solid repeatedly redissolved in toluene and concentrated under reduced
pressure until all traces of thionyl chloride were removed. The resulting
yellow solid (3.9 g) was treated with activated charcoal in boiling
toluene and filtered. The filtrate was concentrated to about 25 mL. Upon
cooling, 4,4'-dicarbonyl chloride-2,2'-bipyridine (2.6 g, 67%)
crystallized out of the filtrate as-an off-white solid, mp
142.degree.-144.degree. C. Anal. Calcd for C.sub.12 H.sub.6 N.sub.2
Cl.sub.2 O.sub.2 : C, 51.27; H, 2.15; N, 9.97. Found: C, 51.32; H, 2.27;
N, 9.54.
A flask contained in a drybox was charged with 0.0703 g (0.25 mM) of
4,4'-dicarbonyl chloride-2,2'-bipyridine and 50 mL of acetonitrile the
solution heated to boil to facilitate dissolution. 50 mL of acetonitrile
was added and the solution cooled to room temperature. An excess portion
(100 .mu.L used; 69 .mu.L, 0.50 mMoles required) of triethylamine (Aldrich
Gold Label) (the triethylamine previously dried through a column of
Activity I alumina) was added followed by addition of 89 .mu.L (0.50 mM)
of 3-(trimethoxysilyl) propylamine (Huls America--Petrarch Systems).
Acetonitrile was added to increase the mixture volume to 250 mL and the
reaction flask shaken. Ultraviolet absorption spectroscopy of the pale
yellow solution confirmed coupling of 4,4'-dicarbonyl
chloride-2,2'-bipyridine and 3-(trimethoxysilyl) propylamine to provide
4,4'-(di(carboxylic
acid-(N-3-(trimethoxysilyl)propyl)amide))-2,2'-bipyridine, having
molecular formula C.sub.24 H.sub.38 O.sub.8 N.sub.4 Si.sub.2, the compound
referred to herein as "UTF-14B3".
A fused silica slide was cleaned by the Standard Cleaning Method and placed
in the pale yellow solution of the UTF-14B3 compound. The solution was
heated to 60.degree. C. over a 40 minute period. The slide was then
removed, rinsed twice in acetonitrile and baked for 3 minutes at
120.degree. C. on a hotplate. After heating, the coated slide provided a
contact angle of about 15.degree.. Ultraviolet absorption spectroscopy
confirmed the binding of the UTF-14B3 compound to the slide surface and
indicated a film thickness on the slide of between 1 and 2 molecular
layers.
EXAMPLE 5
This example illustrates the binding of a palladium electroless
metallization catalyst to the UTF-14B3 compound by a sequential addition
process.
A 0.002M acetonitrile solution of the UTF-14B3 compound was prepared as in
Example 4. Added to this solution was an equal volume of a 0.002M
acetonitrile solution of bis(benzonitrile)palladium dichloride.
Ultraviolet absorption spectroscopy confirmed the binding of the palladium
compound to the UTF-14B3 compound via the observation of new, broad
absorption bands at about 220 nm and 327 nm characteristic of the
catalyst-ligand complex.
EXAMPLE 6
This example illustrates the binding of a palladium electroless
metallization catalyst to the UTF-14B3 compound by a simultaneous addition
process.
A flask in a drybox was charged with 4,4'-dicarbonyl
chloride-2,2'-bipyridine, 3-(trimethoxysilyl)propylamine,
bis(benzonitrile)palladium chloride and triethylamine in a respective
concentration ratio of 0.1 mM: 0.2 mM: 0.1 mM: 0.25 mM. 50 mL of
acetonitrile was added to dissolve the solid. Acetonitrile was then added
to increase the volume of the solution to 100 mL. Ultraviolet absorption
spectroscopy of the red-orange solution matched the spectrum of Example 5
confirming formation of the UTF-14B3 compound and the binding thereto of
the palladium catalyst.
EXAMPLE 7
This example illustrates metallization of substrate surfaces according to
the processes of the invention.
A fused silica slide was coated with the UTF-14B3 compound as in Example 4
and then immersed in a solution of 84 mg of PdCl.sub.2 per liter of 0.1M
HCl aqueous solution. The solution was gently stirred for 40 minutes and
the slide then removed and rinsed twice in water. Ultraviolet absorption
spectrum showed strong, broad absorption bands at 220 nm (.epsilon.=70000
M.sup.-1 cm.sup.-1) and a weaker band at 327 nm (.epsilon.=9800 M.sup.-1
cm.sup.-1) indicating binding of the catalyst. These bands were in
agreement with those observed for the UTF-14B3 complex of PdCl.sub.2 in
acetonitrile (note Examples 5 and 6) and indicate that the surface-bound
and solution phase complexes are similar. It was found that greater than
95 percent of the ligating sites of the UTF-14B3 surface had accepted a
PdCl.sub.2 species. A time dependence study of the uptake of PdCl.sub.2
from the catalyst solution by the UTF-14B3 surface film was performed. The
absorption intensity at 220 rim, which is proportional to the level of
UTF-14B3 bound PdCl.sub.2 in the film, was determined as a function of the
exposure time of the UTF-14B3 film to the PdCl.sub.2 /HCl solution. The
results showed that about 85% of the ligating sites had accepted the
PdCl.sub.2 catalyst after 15 minutes exposure of the UTF-14B3 film to the
solution.
EXAMPLE 8
This example illustrates the binding rate of the metallization catalyst
from solution by the substrate ligating group can be dependent on the
nature of the metallization catalyst solution.
A UTF-14B3 coated fused silica slide prepared as in Example 4 was treated
with a solution of 11 mg of bis(benzonitrile) palladium dichloride in 100
mL of tetrahydrofuran. Ultraviolet spectrum absorption bands at 220 nm and
327 nm were observed following treatment indicating formation of the
UTF-14B3 complex of PdCl.sub.2 in the surface film. A time dependence
binding study as per Example 7 indicated that binding was greater than 90%
complete after a 5 minute treatment of the film with the catalyst
solution. The time necessary to achieve a comparable degree of binding
using the PdCl.sub.2 /0.1M HCl (aq) solution of Example 7 was greater than
15 minutes.
EXAMPLE 9
This example illustrates the metallization of a substrate in accordance
with the present invention.
A fused silica slide coated with UTF-14B3 as in Example 4 was treated with
PdCl.sub.2 /0.1M HCl (aq) solution for 40 minutes as described in Example
7. The treated slide was water rinsed and placed in 25% Co Metallization
Bath with gentle agitation for 4 minutes. Hydrogen gas evolution and
metallization of the slide were observed during this time. A thin,
homogeneous, mirror-like plate of Co metal was observed over the entire
treated area of the slide. The slide was removed from the metallization
bath, water rinsed twice and dried under nitrogen. Treatment of a fused
silica slide uncoated with UTF-14B3 by the same procedure gave no
metallization. Similarly, treatment of a UTF-14B3 coated fused silica
slide with the 25% Co Metallization Bath, but without prior treatment with
metallization catalyst solution, gave no metallization.
EXAMPLE 10
This example illustrates binding of a metallization catalyst directly to a
substrate surface.
An n-type, native oxide silicon wafer (available from Monsanto Co., St.
Louis, Mo.) was cleaned by the Standard Cleaning Method and placed in a
wafer carrier within a beaker. A fresh 0.001M acetonitrile solution of the
UTF-14B3 complex of PdCl.sub.2 of Example 6 was added to the beaker, and
the solution was allowed to stand at room temperature for 1.5 hours. The
wafer was then removed, rinsed twice with fresh acetonitrile and baked for
3 minutes on a hotplate at 120.degree. C. The wafer was then immersed in
the 25% Co Metallization Bath for 4 minutes, rinsed twice with water and
dried under nitrogen. A Co metal plate was observed over the entire area
of the wafer treated with the catalyst solution. Treatment of a clean
silicon wafer uncoated with the UTF-14B3 complex of PdCl.sub.2 with the
25% Co Metallization Bath did not provide a metal deposit.
EXAMPLE 11
This example illustrates removal of metallization catalyst bound to outer
layers of a bulk surface ligating film. Reactivation of the resulting
de-catalyzed film with additional metallization catalyst solution permits
metallization of the surface.
A fused silica slide coated with a bulk film of
.beta.-trimethoxysilylethyl-2-pyridine from Example 3 was treated with
PdCl.sub.2 /0.1M HCl (aq) solution for 15 minutes as described in Example
7. Ultraviolet absorption spectroscopy of the treated slide showed an
absorption band at 235 nm in addition to bands at about 200 nm and 260 nm.
The 235 nm band is indicative of a surface bound
.beta.-trimethoxysilylethyl-2-pyridine complex of PdCl.sub.2. The presence
of the bands associated with the free surface bound
.beta.-trimethoxysilylethyl-2-pyridine indicated that not all ligation
sites within the film had complexed PdCl.sub.2. The fused silica slide was
then immersed in heated tetrahydrofuran as described in Example 3. After
removal of the slide from the tetrahydrofuran bath, ultraviolet absorption
showed an absence of the surface bound PdCl.sub.2 as evidenced by the
disappearance of the 235 nm band. Failure of an identically treated slide
to metallize upon immersion in the 25% Co Metallization Bath confirmed the
absence of metallization catalyst on the surface. The remaining absorption
bands at 200 nm and 260 nm were consistent in intensity and position with
those observed for ligation films of approximate monomolecular average
thickness described in Example 1. Subsequent treatment of this slide with
fresh metallization catalyst solution restored the 235 nm absorption band
to the spectrum and, upon immersion of the slide in the 25% Co
Metallization Bath, Co metal deposited on the slide.
EXAMPLES 12-18
These examples illustrate control of catalytic activity and stability of a
metallization catalyst through formulation of catalyst solutions
comprising specific additives. Each solution of the examples was tested
for metallization selectivity as follows. An n-type, native oxide silicon
wafer was dip coated with .beta.-trimethoxysilylethyl-2-pyridine. This
wafer and a second uncoated n-type, native oxide silicon wafer were each
treated with the described catalyst solution for 15 minutes and water
rinsed twice. Each wafer was then immersed in the 25% Co Metallization
Bath for 4 minutes, water rinsed twice and dried under nitrogen. Each
wafer was then examined for evidence and quality of metallization. Plating
is considered selective if the coated wafer was metallized but no
metallization of the uncoated wafer was observed. Plating is considered
non-selective if both wafers metallize.
EXAMPLE 12
An electroless metallization catalyst solution preferred for its stability
and catalytic activity and selectivity, was prepared as follows: a vessel
was charged with 11 mg of Na.sub.2 PdCl.sub.4 .times.3H.sub.2 O in 1 mL of
1.0M NaCl (aq) and water added to bring the volume of the mixture to 100
mL. The resulting clear green-yellow solution was initially inactive as a
metallization catalyst. After standing at room temperature for 24 hours,
the solution turned a deeper yellow color and exhibited high activity and
selectivity as a Co metallization catalyst. Both catalyst activity and
selectivity of the solution were maintained for more than 30 days without
further treatment.
EXAMPLE 13
A solution was prepared by dissolving 8.6 mg. of Na.sub.2 PdCl.sub.4
.times.3H.sub.2 O in 100 mL water. Immediately after preparation, this
solution exhibited selective Co metallization. However, the solution was
unstable and decomposed within hours via precipitation of
palladium-containing oligomers.
EXAMPLE 14
A solution was prepared by adding 10 mL of an aqueous 0.1M
tetraethylammonium chloride solution to 11 mg of Na.sub.2 PdCl.sub.4
.times.3H.sub.2 O in a 100 mL volumetric flask and diluting to the mark
with water. The clear, yellow solution had pH 4.5 and was an active and
selective Co metallization catalyst within one hour of preparation. Within
24 hours of preparation, this solution acquired a dull, dirty yellow color
and visually exhibited evidence of faint particulate matter. The solution
pH was approximately 4.2 at this time. The solution filtered through 0.22
.mu.m cellulose filters as well as unfiltered solution gave selective
metallization. After 48 hours from preparation, the solution contained a
solid precipitate and was unusable as a metallization catalyst.
EXAMPLE 15
An aqueous acetate buffer solution was prepared which was 0.5M initially in
both sodium acetate and acetic acid. 2 mL of this solution was added to 11
mg of Na.sub.2 PdCl.sub.4 .times.3H.sub.2 O in a 100 mL volumetric flask
and the flask diluted to the mark with water. The solution was clear,
green-yellow in color with pH 4.6 and was initially inactive as a
metallization catalyst. Within 24 hours of preparation, the solution
yellowed and became an active, though nonselective, metallization
catalyst. Filtering as described for the solution of Example 14 did not
affect the behavior of the solution. Solution pH remained stable (in the
range of 4.6 to 4.7) for at least 2 days following preparation.
EXAMPLE 16
100 mL of the active catalyst solution of Example 12 was prepared, and 2 mL
of the solution was removed and replaced with a 2 mL aliquot of a 0.5M
acetate aqueous buffer which was 0.5M in both sodium acetate and acetic
acid. The resulting clear, yellow solution had pH 4.55 and was an active,
selective Co metallization catalyst. The solution remained an active,
selective metallization catalyst for at least 2 days following its
preparation, at which time it was yellow in color with pH 4.5.
EXAMPLE 17
A solution was prepared by simultaneous addition of 1 mL of NaCl (aq)
solution and 2 mL of 0.5M acetate aqueous buffer solution (the buffer
solution 0.5M in both sodium acetate and acetic acid) to 11 mg solid
Na.sub.2 PdCl.sub.4 .times.3H.sub.2 O in a 100 mL volumetric flask.
Following dissolution of the solid, the flask was diluted to the mark with
water. The clear, green-yellow solution had pH 4.7. Although the pH
remained stable at this value for at least 7 days, the solution exhibited
no activity as a metallization catalyst during this time. The activity of
the solution as a metallization catalyst increased slowly during the
following 3 to 4 days. Approximately 11 days after preparation, the
solution reached full activity as a selective Co metallization catalyst.
EXAMPLE 18
A solution was prepared by dissolving 11 mg of Na.sub.2 PdCl.sub.4
.times.3H.sub.2 O in 10 mL of 0.01M NH.sub.4 Cl (aq) solution. The clear,
green-yellow solution was inactive as a metallization catalyst for at
least 2 days following preparation. A drop in pH from 3.8 to 3.5 occurred
during this time.
EXAMPLE 19
This example illustrates that a substrate requires a suitable ligating
group for the substrate to be metallized in accordance with the present
invention.
Three n-type, native oxide silicon wafers were cleaned by the Standard
Cleaning Method. The first wafer was dip coated with
.epsilon.-trimethoxysilylethyl-2-pyridine as in Example 1. The second
wafer was coated with a film of 4-chloromethylphenyltrimethoxysilane using
the surface silanization procedure described in Example 1. Contact angles
of 45.degree. (first wafer) and 70.degree. (second wafer) were obtained
indicative of coating of the wafer surfaces. The third wafer was not
coated and provided a contact angle of approximately 5.degree..
Each of the wafers was immersed in the active catalyst solution of Example
12 for 15 minutes, water rinsed and then immersed in the 25% Co
Metallization Bath for 4 minutes. The wafers were removed from the Co
bath, water rinsed and dried under nitrogen. A full, homogeneous,
mirror-like plate of Co metal was observed on the
.beta.-trimethoxysilylethyl-2-pyridine coated wafer in areas treated with
the catalyst solution. No Co metal plate was observed on either of the
other wafers.
EXAMPLE 20
This example illustrates selective electroless metallization according to
the present invention.
Two n-type, thermal oxide (350 angstrom oxide thickness) silicon wafers
were cleaned by the Standard Cleaning Method and coated with
.beta.-trimethoxysilylethyl-2-pyridine as in Example 1. Film integrities
were confirmed by contact angle measurements. The wafers were patterned
with a serpentine mask using ultraviolet exposure with Karl Suss Model MJB
3 Contact Printer equipped with Karl Suss Model 507X Xenon Lamp (254 nm).
LrV power level was 6.0 mW/cm.sup.2 at 254 nm and exposure time was 15
minutes. The first wafer was treated with the active catalyst solution of
Example 12, and metallized by immersing the wafer in the 25% Co
Metallization Bath for 4 minutes. The second wafer was treated with the
Pd/Sn colloidal catalyst identified as Cataposit 44 (Shipley Company,
Newton, Mass.) and metallized with cobalt by standard procedures. Each
wafer was examined under an optical reflection microscope. For the wafer
treated with the solution of Example 12, the completeness of metallization
in the plated regions and the lack of debris in the clear fields were
superior compared to the same characteristics of the wafer metallized with
the Cataposit 44 catalyst.
EXAMPLE 21
This example illustrates the ability to control the adhesion of a metal
plate to an underlying substrate by variation of the chemical bond
strength between the metallization catalyst and surface ligating groups.
Two n-type, native oxide silicon wafers were cleaned by the Standard
Cleaning Method. The first wafer was dip coated with the
.beta.-trimethoxysilylethyl-2-pyridine solution as described in Example 1.
The second wafer was treated by the UTF-14B3 compound as described in
Example 4. Each wafer was treated for 15 minutes with the active catalyst
solution of Example 12, water rinsed twice, and immersed in the 25% Co
Metallization Bath for 4 minutes. The wafers were removed from the bath,
water rinsed and dried under nitrogen. Complete, homogeneous, mirror-like
plating of Co metal was observed on each wafer where exposed to the
catalyst solution. Measurement by Dektak profilometry showed plating on
each wafer of equal thickness (350.+-.50 angstroms). A piece of Scotch.TM.
brand adhesive tape was placed on the plated areas of each wafer. The tape
was removed from each wafer in a slow steady manner. Tape removal lifted
between about 50-70% of the Co metal film as flakes from the wafer treated
with the .beta.-trimethoxysilylethyl-2-pyridine compound. No Co metal was
removed from the second wafer coated with the UTF-14B3 compound after
numerous applications and removals of tape.
EXAMPLE 22
This example illustrates the ability to deposit thick films of highly
stressed materials by the processes of the invention.
The procedure of Example 21 was repeated, except immersion of the wafers in
the 25% Co Metallization Bath was increased from 4 minutes to 50 minutes.
Severe and nearly total flaking of the Co plate on the
.beta.-trimethoxysilylethyl-2-pyridine coated wafer was observed after
about 5 to 10 minutes in the metallization bath. A homogeneous, adherent,
mirror-like Co metal plate was observed on the UTF-14B3 coated wafer even
after 50 minutes in the Co bath. Dektak profilometry showed a metal
thickness of 2750.+-.250 angstroms for this second wafer. Application and
removal of Scotch.TM. brand tape as in Example 21 did not remove Co from
the second wafer.
EXAMPLE 23
This example illustrates modification of a tungsten metal surface by the
method of the invention.
Three CVD tungsten on silicon wafers were cleaned by immersion in a 30%
H.sub.2 O.sub.2 (aq) solution for 1 hour and then water rinsed. The first
wafer was dip coated with .beta.-trimethoxysilylethyl-2-pyridine as in
Example 1 and the second wafer was coated with UTF-14B3 as in Example 4.
The third wafer was not coated and used as a control. Each wafer was
immersed in the Catalyst Solution 2 as prepared in Example 28 herein for
15.minutes, water rinsed and then immersed for four minutes in the 25% Co
Metallization Bath. Each wafer was then water rinsed and dried under
nitrogen. Homogeneous Co plates were observed for the first and second
coated Co tungsten wafers, but no metallization was observed for the third
control wafer. Scotch.TM. tape adhesion tests as described in Example 21
showed greater metal adhesion for the UTF-14B3 coated wafer than for the
.beta.-trimethoxysilylethyl-2-pyridine coated wafer.
EXAMPLE 24
This example illustrates the ability to plate surfaces with nickel by the
method of the invention.
A thermal oxide SiO.sub.2 wafer was dip coated with
.beta.-trimethoxysilylethyl-2-pyridine as in Example 1. The coated wafer
was treated with Catalyst Solution 2 (as prepared in Example 28 herein)
for 0.5 hours. The wafer was water rinsed and then immersed for 20 minutes
in the nickel electroless metallization solution identified as Niposit 468
(Shipley Company). This nickel metallization solution was heated to
25.degree. C. and formulated according to manufacturer's instruction and
diluted to 5% strength. A homogeneous nickel deposit was obtained over the
entire area of wafer contacted by the catalyst solution. A clean thermal
oxide SiO.sub.2 wafer that was not coated with the
.beta.-trimethoxysilylethyl-2-pyridine was subjected to the above
procedures but nickel did not deposit on the uncoated wafer.
EXAMPLE 25
This example illustrates distributing ligating moieties throughout a
substrate according to the present invention.
A poly(4-vinylphenol) (PVP, average molecular weight=5000 g/mol) stock
solution was prepared by sonicating a mixture of 26 g of PVP and 74 g of
diglyme. 125 mg of 4,4'-dimethyl-2,2'-bipyridine were dissolved in 10 mL
of the PVP stock solution. A film of this solution was spin coated at 4000
rpm for 30 seconds onto a clean, n-type native oxide silicon wafer. A
control was prepared by spin coating by identical procedure the PVP stock
solution onto a clean, n-type native oxide silicon wafer. The two coated
wafers were baked at 90.degree. C. for 0.5 hours. Each coated wafer was
treated with the active catalyst solution of Example 12 for 60 minutes,
water rinsed twice and immersed in the 25% Co Metallization Bath for 4
minutes with agitation. The wafers were then water rinsed and dried under
nitrogen. A complete, homogeneous, plate of Co was observed on the wafer
coated with the bipyridine solution in regions contacted with the catalyst
solution. No metallization of the control wafer was observed.
EXAMPLE 26
This example illustrates metallization of a material which inherently
contains ligating moieties.
Two 100 mg samples of neutral alumina (Fisher Scientific; 80-200 mesh
powder; Brockman activity I) were placed in separate vessels. The samples
were each equilibrated in water by washing thoroughly with three 50 mL
portions of water. The first sample was maintained under water as a
control and the second sample treated for 15 minutes with the active
catalyst solution of Example 12, with occasional stirring. Each sample was
decanted and washed separately with 6 portions of water and then dried for
2 minutes on a suction funnel after the final wash. The 100% Co
Metallization Bath was then added to each sample and the resulting
slurries stirred for 60 minutes. For the sample treated with the active
catalyst solution of Example 12, vigorous H.sub.2 evolution was observed
during stirring, and the resulting gray-black Co metallized alumina
particles were magnetic. No evidence of metallization of the control
sample was observed.
EXAMPLE 27
This example illustrates metallization of ceramic material according to the
processes of the invention.
The Nextel fibers (3M Corp.) employed in this example were ceramic
composite fibers composed of alumina, boria and silica coated with a
polymeric substance. Metallized samples of these fibers have numerous
applications, including as absorbers of electromagnetic radiation.
Three one inch strands of Nextel Roving 312, Type 1800D Ceramic Fibers were
employed. The first strand was used without further treatment. The second
strand was flame cleaned to remove the polymeric surface coating. The
third strand was cleaned by the Standard Cleaning Method. Each strand was
water rinsed twice and immersed in the active catalyst solution of Example
12 for 15 minutes. The strands were removed from the solution and
repeatedly water rinsed to remove the catalyst solution. The strands were
then metallized using the 50% Co Metallization Bath. In each case,
hydrogen evolution and fiber darkening indicated metallization of each of
the fibers was observed within the first two minutes of exposure to the Co
bath. Metallization of the first strand is stopped after 7 minutes by
quenching with water. The metallic gray fibers were dried under nitrogen
and shown to be magnetic by their attraction to a permanent magnet.
Metallization of the second and third strands was allowed to proceed for
60 minutes prior to quenching. In each case, the magnetic, metallic gray
fibers were obtained. Some flaking of the Co metal from the flame cleaned
strand was noticed during the aqueous wash of those fibers following
metallization. No flaking of Co metal from the third strand (Standard
Cleaning Method) was observed. Repetition of these procedures using
strands which had not been treated with the active catalyst solution of
Example 12 gave no Co metallization. No Co metallization was observed upon
repetition of the procedure using ceramic fibers not treated with the
catalyst solution.
EXAMPLE 28
This example illustrates preparation of metallization catalyst solutions in
accordance with the invention-at pH values greater than 4, and
stabilization of the solutions by control of chloride ion concentrations.
Three catalyst solutions were prepared as follows. Into each of three 100
mL volumetric flasks was added 11.3 mg Na.sub.2 PdCl.sub.4 3H.sub.2 O. A 1
mL aliquot of 1M NaCl (aq) solution was added to the first two flasks,
which were designated as Solutions 1. and 2 respectively. A 2 mL aliquot
of 1M NaCl (aq) solution was added to the third flask, which was
designated as Solution 3. After dissolution of solids, a 10 mL aliquot of
the MES Solution A having pH of 4.9 was added to each of the three
solutions, and each flask was diluted with water to a volume of 100 mL.
Three silicon wafers were dip coated with
.beta.-trimethoxysilylethyl-2-pyridine as in Example 1 and were each
treated with one of the catalyst Solutions 1, 2 and 3, rinsed twice with
water, and then immersed in the 25% Co Metallization Bath for 4 minutes.
None of the wafers were metallized.
After allowing the three catalyst solutions to stand overnight, three
silicon wafers dip coated with .beta.-trimethoxysilylethyl-2-pyridine were
again each treated with one of catalyst Solutions 1, 2 and 3, rinsed twice
with water, and immersed in the 25% Co Metallization Bath for 4 minutes.
Full metallization was observed for the wafers treated with Solutions 1
and 2. No metallization was observed for the wafer treated with Solution
3. Uncoated silicon wafers that were treated with Solutions 1, 2 and 3
also did not metallize.
A 10 mL aliquot of Solution 2 was then removed and replaced with a 10 mL
aliquot of 1.0M NaCl (aq) solution. The approximate compositions expressed
in terms of initial components of the solutions are shown in the Table
below:
______________________________________
Solution
[Cl.sup.- ]
pH [MES] mg Pd/0.1 L
______________________________________
1 0.01 M 4.84 0.01 M 11.3
2 0.099 M 4.84 0.009 M 10.3
3 0.02 M 4.88 0.01 M 11.3
______________________________________
The concentrations of total MES and Pd.sup.2+ in the solutions are
equivalent to within 10%. The principal differences involve total chloride
ion concentrations. The pH of solutions 1-3 remain in the range of 4.65 to
4.90 during the lifetime of these experiments.
Catalytic activity of each solution was monitored daily via treatment of
.beta.-trimethoxysilylethyl-2-pyridine coated and uncoated Si wafers with
each solution followed by metallization with the 25% Co Metallization
Bath. Solution 1 served as a control. It exhibited selective metallization
of coated Si wafers for about 7 days following preparation. Thereafter,
the solution loses its ability to catalyze metallization of wafer surfaces
and eventually produced a brown precipitate. Solution 2 (as modified)
continued as an active, selective metallization catalyst for about 1 month
and no precipitation was observed. Addition of a large chloride ion
aliquot to catalytically active Solution 1 can therefore provide at least
a four-fold increase in solution stability. Solution 3 slowly increased in
catalytic activity with time and full activity was reached about 4 to 5
days after solution preparation. The solution remained an active,
selective metallization catalyst for at least one month after preparation.
In this case, a two-fold increase in chloride ion concentration at the
time of solution preparation can also prolong the useful life of the
catalyst solution. However, addition of more Cl.sup.- at the time of
solution preparation also increases the time to reach full activity.
Stable catalyst solutions can be prepared at pHs significantly greater
than pH of 4 using these methods. For example, catalyst solutions stable
at pH of about 5.7 or 6.4 can be prepared following the method described
for Solution 2 above using MES Buffer Solutions B or C, respectively, in
place of MES Buffer Solution A.
EXAMPLE 29
This example illustrates control of the minimum contact time between a
metallization catalyst solution and substrate necessary to provide
complete substrate metallization. Control is achieved by adjustment of
catalyst composition and age.
"Minimum solution contact time" is defined for this example as the time
necessary for a catalyst solution to contact a
.beta.-trimethoxysilylethyl-2-pyridine coated wafer to yield full and
selective metallization on the wafer following a water rinse and
subsequent 4 minute treatment with the 25% Co Metallization Bath.
A variety of catalyst solutions were prepared as described in the Table
below. The composition represented by Solution 1 in the Table is identical
to that described in Example 12. Solutions 2 and 3 were prepared using MES
Buffer Solutions B and C, respectively, by following the procedures
described in Example 28. Solution 4 represents a more aged version of
Solution 3. Solution age (Soln. Age) was measured from initial catalyst
dissolution at solution preparation.
__________________________________________________________________________
Soln
[Cl.sup.- ]
[MES] mg Pd/0.1L
Soln. Age
pH Min. Time
__________________________________________________________________________
1 0.01 M
0 11.3 10 days
3.7
.gtoreq.10 min.
2 0.118 M
0.009 M
10.3 2 days
6.3
1 min.
3 0.11 M
0.009 M
10.3 2 days
5.7
3 min.
4 0.11 M
0.009 M
10.3 30 days
5.7
2 min.
__________________________________________________________________________
As shown in the above Table, control of the minimum contact time can be
achieved by variations in the catalyst solution composition and age. For
Solution 1 aged 10 days, minimum solution contact time was greater than or
equal to 10 minutes. For Solution 2 aged 2 days, minimum solution contact
time was 1 minute. For Solution 3 aged 2 days, minimum solution contact
time was 3 minutes. For Solution 4 aged 30 days, minimum solution contact
time was 2 minutes.
EXAMPLE 30
This example illustrates chemical modification of a substrate surface to
provide functional groups capable of ligating an electroless metallization
catalyst.
A one inch square, 2 mm thick piece of high-density polyethylene with
contact angle of 83.degree. was placed for 1.5 hours in a 70.degree. C.
acidic dichromate solution consisting of 9.2 g of K.sub.2 Cr.sub.2 O.sub.7
and 80 mL of concentrated H.sub.2 SO.sub.4 in 46 mL of water. The solution
was then cooled to room temperature over 1.5 hours, and the polymer
removed and sequentially washed with 5 portions water, 2 portions acetone
and 2 portions toluene. After washing, the polymer had a contact angle of
63.degree. C. The polymer was immersed for 20 minutes in a saturated
solution of bis (benzonitrile) palladium dichloride in toluene, and then
rinsed with toluene and dried under nitrogen. The sample was then immersed
in the 50% Co Metallization Bath for 4 minutes, rinsed twice with water
and dried under nitrogen. A mirror-like, adherent plate of Co metal was
deposited over the entire area treated with the catalyst solution. A
second one inch square, 2 mm thick piece of high-density polyethylene was
subjected to the same procedure, except the second polymer square was not
contacted with the dichromate bath. No metallization of the second square
was observed.
EXAMPLE 31
This example illustrates metallization of a polymer substrate by binding a
ligating film to the polymer surface according to the present invention.
Two one inch square, 2 mm thick pieces of polyethersulfone (contact angle
53.degree.) were oxidized in a dichromate bath as described in Example 30.
Following successive rinses of the samples with 5 portions of water, 2
portions of acetone and 2 portions of toluene (contact angle now
64.degree.), the samples were dried under nitrogen and one sample was
exposed to the active catalyst solution of Example 12 for 15 minutes.
Metallization of the thus treated polyethersulfone was attempted as
described in Example 30 for polyethylene. No metallization of the
polyethersulfone oxidized surface occurred indicating that dichromate
oxidation did not generate functional groups capable of ligating with the
metallization catalyst. The second piece of oxidized polyethersulfone was
dip coated with .beta.-trimethoxysilylethyl-2-pyridine. This second
polyethersulfone sample has a contact angle of about 50.degree. after
coating. Treatment of this second polyethersulfone sample with the active
catalyst solution of Example 12, and the 25% Co Metallization Bath as
described above provided a Co plate on that portion of the surface
contacted by the metallization catalyst solution. The Co metal plate was
dull and gray in color but was full and homogeneous. Treatment of a
polyethersulfone sample which had not been oxidized with dichromate or
coated with the ligating film gave no metallization.
EXAMPLE 32
This example illustrates the construction of a metallizable film on a
substrate surface by sequential addition of surface adsorbent component,
ligating component and metallization catalyst to the surface.
A clean fused silica slide was coated with a methanol solution 1.0 mM in
acetic acid and containing 1% (v/v) 3-(trimethoxysilyl)propylamine
(referred to herein as UTF-14) by dip coating. The coated slide had a
contact angle of about 30.degree.. Ultraviolet absorption spectrum showed
a weak peak at 200 nm indicative of the chemisorbed silyl propylamine
compound. A solution containing 100 mg of 8-quinoline sulfonic acid
chloride (referred to herein as UTF-QS) and 300 .mu.L of triethylamine
(the triethylamine previously dried through a column 0f Activity I
alumina) in 20 mL of acetonitrile was added to a Coplin jar containing the
coated slide. The orange solution was occasionally mixed, and after 1
hour, the slide was removed and rinsed with acetonitrile and dried under
nitrogen. The dried slide had a contact angle of about 56.degree..
Ultraviolet absorption spectrum showed bands at about 215 nm and 280 nm.
These bands were consistent with those observed for the UTF-14QS compound
in acetonitrile solution (.lambda.=214 nm, .epsilon.=45500M.sup.-1
cm.sup.-1 ; .lambda.=276 nm, .epsilon.=6000M.sup.-1 cm.sup.-1) confirming
the binding of the quinoline sulfonic acid chloride to the silyl
propylamine coated surface. The value of .epsilon.=6000M.sup.-1 cm.sup.-1
obtained at 215 nm for the coated surface suggested greater than 20
percent surface coverage of the UTF-14QS compound.
The slide coated with the UTF-14QS compound was then immersed in the active
catalyst solution of Example 12 for 0.5 hour, water rinsed and dried under
nitrogen. Ultraviolet absorption spectrum of the thus treated slide was
indicative of binding of the catalyst, showing a strong absorption at 210
nm (.epsilon.=32000M.sup.-1 cm.sup.-1) and broad shoulder at about 290 nm
(.epsilon.=13000M.sup.-1 cm.sup.-1). Catalyst ligation was confirmed by
treatment of the slide with the 25% Co Metallization Bath for 4 minutes. A
smooth, full, mirror-like Co plate was obtained over the entire surface of
the slide treated with the catalyst solution. A similarly prepared slide
coated with the UTF-14QS compound, but which had not been exposed to a
metallization catalyst, was not metallized upon treatment with the Co
solution.
EXAMPLE 33
This example illustrates the ability to metallize substrates modified with
a chelating group comprising the ethylene diamine function by the method
of the invention.
Glass microscope slides were cleaned via the Standard Cleaning Method.
N-2-aminoethyl-3-aminopropyltrimethoxysilane, of formula (CH.sub.3
O).sub.3 SiCH.sub.2 CH.sub.2 CH.sub.2 NHCH.sub.2 CH.sub.2 NH.sub.2
(referred to herein as UTF-EDA), was used as received from Huls of America
(Bristol, Pa.) and was used as the surface coating applied to the slides.
The clean glass slides were treated by immersion for 15 minutes at room
temperature in a solution consisting of 250 mL of freshly mixed 94% vol.
acidic, anhydrous methanol (Aldrich Sure-Seal containing 1.0 mM acetic
acid), 5% vol. water, and 1% vol. UTF-EDA. The slides were removed from
the treatment solution, rinsed twice in methanol and baked for 5 minutes
at 120.degree. C. on the surface of a hotplate to remove residual solvent.
Contact angles were about 17.degree. for the freshly prepared slides. The
contact angles slowly increased with time and reached stable values of
about 30.degree. within 12 hours after sample preparation.
A clean, blank slide uncoated by UTF-EDA serving as a control and a UTF-EDA
coated slide as prepared above were each treated for 30 minutes with the
metallization catalyst described as Solution 1 of Example 28. The age of
the catalyst solution was 3 days and its pH was 4.9. Each of the slides
was then rinsed three times with water and immersed in a 25% Co
Metallization Bath for 7 minutes. A homogeneous, mirror-like Co metal
plate was observed over the entire region of the UTF-EDA coated slide
treated by Solution 1. A complete absence of metallization on the control
slide indicated that the metallization of the UTF-EDA coated slide was
selective. Application of the Scotch.TM. tape adhesion test to the Co
metal plate resulted in complete adherence of Co metal to the slide. This
indicates that UTF-EDA films catalyzed and metallized by the method of the
invention exhibit superior adhesion of Co metal films compared to the
.beta.-trimethoxysilylethyl-2-pyridine films described in Example 21.
EXAMPLE 34
This example illustrates the ability to use organotitanate materials to
provide the adhesive functions in preparing a surface which is
metallizable by the method of the invention.
The adhesive/chelating agent 2-propanolato-tris
(3,6-diaza)-hexanolato-titanium (IV), of chemical formula
HC(CH.sub.3).sub.2 OTi[O(CH.sub.2).sub.2 NH(CH.sub.2).sub.2 NH.sub.2
].sub.3 (referred to herein as UTF-44) was used as received from Kenrich
Petrochemicals, Inc. (Bayonne, N.J.). A surface treatment solution was
prepared by dissolving 3.7 g of UTF-44 in a 250 mL volumetric flask
containing 100 mL of 2-propanol and diluting to the mark with 2-propanol.
Native oxide n-type silicon wafers were cleaned by the Standard Cleaning
Method and immersed in this solution. The solution containing the wafers
was placed on a hotplate and brought to 60.degree. C. over the course of
60 minutes. The solution remained clear during this time. The treated
wafers were removed, rinsed twice in 2-propanol, dried under nitrogen, and
baked for 3 minutes at 120.degree. C. on a hotplate. Contact angles of
16.degree. were obtained on the freshly prepared wafers. Contact angles
slowly increased with time and reached a value of 22.degree. approximately
16 hours after baking of the wafers.
One of the UTF-44 coated wafers so prepared was treated for 60 minutes with
a saturated solution of bis(benzonitrile)palladium(II) dichloride in
toluene. The wafer was rinsed twice in toluene and dried under nitrogen. A
clean, blank wafer uncoated by UTF-44 was subjected to identical treatment
and served as a control. Both wafers were immersed in a 25% Co
metallization bath for 4 minutes, rinsed twice in distilled water and
dried under nitrogen. Selective metallization of the UTF-44 coated wafer
was observed as a homogeneous, mirror-like Co metal plate over the area of
the wafer contacted by the bis(benzonitrile)palladium(II)
dichloride/toluene solution.
EXAMPLE 35
This example illustrates the ability to catalyze the UTF-44 film of Example
34 towards Co metallization using an aqueous-based catalyst solution.
A UTF-44 coated wafer prepared as described in Example 34 and a clean,
blank control wafer uncoated with UTF-44 were treated with catalyst
Solution 1 from Example 28 for 60 minutes. The wafers were rinsed twice in
distilled water and then immersed in 25% Co metallization bath for 7
minutes. The UTF-44 coated wafer metallized as a homogeneous, mirror-like
Co metal plate over the region contacted by Solution 1. A Scotch.TM. tape
adhesion test applied to the metal film following aqueous rinse and drying
under nitrogen gave complete adhesion of the metal to the substrate, a
result identical to that described in Example 33.
EXAMPLE 36
This example illustrates the ability to metallize lipid tubule
microstructures through the process of the invention.
The tubules used in this example were grown using
1,2-bis-(10,12-tricosadiynoyl)-sn-glycero-3-phosphorylcholine lipid
(DC.sub.23 PC; JP Laboratories, Inc., Piscataway, N.J.) and the
homogeneous crystallization technique from ethanol/water as disclosed in
U.S. Pat. No. 4,911,981, incorporated herein by reference. The tubules
were dialyzed with water prior to use.
A tubule suspension in water was gravity filtered to remove excess water.
The moist white tubules were placed in a beaker and 15 mL of the active
catalyst solution of Example 12 added with gentle mixing to disperse the
tubules. The mixture was allowed to stand for 1.5 hours with occasional
swirling to maintain suspension of the tubules. The mixture was then
gravity filtered and the tubules gently and thoroughly water washed until
the draining wash water was colorless. The resulting yellow-beige tubules
were then suspended in 20 mL of water and 20 mL of the 50% Co
Metallization Bath added and the mixture swirled. Metallization was to
allowed to proceed for 25 minutes without additional mixing during which
time evolution of H.sub.2 was observed. The metallization solution was
carefully withdrawn by pipette and the metallized tubules washed to the
bottom of the vessel with water. No agglomeration of the tubules was
observed after standing in water overnight. The gray-black Co plated
tubules were magnetic. Microscopic examination (403.times. magnification)
indicated a range in the amount of metallization over the surface area of
the tubules. A control batch of tubules that was not treated with a
metallization catalyst did not metallize upon exposure to the Co
metallization solution.
The foregoing description of the present invention is merely illustrative
thereof, and it is understood that variations and modifications can be
made without departing from the spirit or scope of the invention as set
forth in the following claims.
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